Reconfigurable Series Feed Network for Squint-free Antenna Beamforming Using Distributed Amplifier-Based Negative Group Delay Circuit

A new type of tunable series feed network for squint-free antenna beamforming using microwave distributed amplifier (DA)-based negative group delay (NGD) circuits is proposed. Utilizing the DA-based NGD circuits as delay lines between elements in an antenna array, squint-free beamforming with reconfigurable radiation main beams can be achieved. The tuning mechanism is realized by changing the transistor's transconductance. To achieve this, the transistors placed at each stage of the DA are tuned separately. For the proof of concept, a prototype of a two-stage DA-based tunable squint-free series feed network built and tested. The measurement results show that, the main-beam direction of the antenna array can be successfully tuned while maintaining squint-free within a bandwidth of 100 MHz.